With the constant increase in energy prices, there is a growing need to optimize energy usage and recovery. Moreover, campaigns for increasing awareness of the need to reduce carbon dioxide emissions show the importance of energy recovery.
The principle of energy recovery is conversion of unused energy into electricity. The expansion of a fluid such as gas transforms kinetic energy into mechanical energy. Thus, turbines produce electricity by utilizing the phenomenon of expansion to drive a wheel and produce electricity.
The Rankine cycle constitutes the elementary cycle at an industrial level for producing energy from liquid water/steam. It is composed of the following phases: (i) heating, (ii) evaporation at constant temperature until saturation is attained, (iii) isentropic expansion (ideal case), (iv) condensation at constant temperature and (v) isentropic compression.
The Rankine cycle can be applied to other thermodynamic systems, in particular using fluids other than steam. Organic Rankine cycles make it possible to exploit the properties of these other fluids.
The problems posed by substances depleting the ozone layer of the atmosphere (having ozone depletion potential, ODP) were discussed in Montreal, where the protocol was signed requiring a reduction of the production and use of chlorofluorocarbons (CFCs). Amendments have been made to this protocol, requiring abandonment of CFCs and extending the controls to other products.
Hydrofluorocarbons (HFCs) have replaced CFCs and/or hydrochlorofluorocarbons (HCFCs).
Thus, 1,1,3,3,3-pentafluoropropane (HFC-245fa) has been proposed as fluid for organic Rankine cycle systems in which HFC-245fa is heated at a temperature between 140° F. and 300° F. (60 and 149° C.) (WO 2006/113902).
Document WO 2005/085398 discloses the use of polyfluorinated ethers and polyfluorinated ketones as fluid for converting thermal energy to mechanical energy, in particular for organic Rankine cycle systems, at the critical temperature or above the critical temperature of HFC-245fa (154° C.).
The problem encountered with these polyfluorinated ethers or ketones is the low pressure at the condenser, thus promoting infiltration of air into the installations. The presence of moisture and oxygen in the installations leads to corrosion and to destruction of the mechanical parts.